To generate a long-lived, high-affinity antibody response, B-cells need to obtain cognate help from antigen-specific CD4+ T cells. The ability of B cells to recruit help depends on their ability to internalize the antigen or pathogen, degrade it, and present the derived peptides via their MHC class II proteins. At the core of this proposal is the question of whether B cells in need of CD4 T cell help display a distinct subset of antigen-derived peptides than do the dendritic cells (DC) that initially drive CD4 T cell expansion. We hypothesize that the repertoire of pathogen and antigen-derived peptides displayed by B cells and DC will be distinct and that B cell-presented peptides will be only a subset of that displayed by DC. This incomplete pattern of epitope presentation by B cells will lead to limitations on the participation of CD4 T cells to deliver help for production of high affinity antibodies. The main element that has limited our ability to address this important issue is that antigen-specific B cells for any given antigen are present in exceeding low frequencies in vivo. These exceptionally low frequencies prevent tracking of the B cells and evaluation of their peptide display under normal physiological conditions. We propose to solve this problem by taking advantage of B cell receptor (BcR) transgenic mice where a majority of the B cells express a known, defined immunoglobulin on their cell surface. The goal of the experiments in this proposal is to use molecular engineering to endow an antigenic protein or virus the ability to be specifically recognized by the immunoglobulin receptor of BcR transgenic mice. We will use phage display libraries to identify peptide mimics (mimetopes) that bind selectively to the defined monoclonal immunoglobulin molecule and then transfer these mimetopes to several selected antigens, including influenza A virus. This strategy will allow selective targeting of the antigen or virus to the antigen-specific immunoglobulin receptor transgenic B cells. Successful derivation of these unique reagents will allow us to assess CD4 T cell epitope generation after immunoglobulin-mediated uptake of virus or antigen by B cells. Most importantly, use of the derived antigens and the B cell receptor transgenic mice will greatly enhance our ability to understand the interaction between influenza virus and antigen-specific B cells and cognate interactions between B cells and CD4 T cells in vivo. PUBLIC HEALTH RELEVANCE: For vaccination to be successful in eliciting a protective antibody response to pathogen challenge, B lymphocytes need to be able to recruit "help" from another lineage of lymphocytes called T cells. Our experiments are aimed at generating several key experimental tools that will allow us to dissect and ultimately control the focus of T cells, to allow them to more efficiently provide help to antibody producing cells. Through these experiments, we will gain the insight needed to improve vaccine efficacy.